Lights at Night Linked to Breast Cancer

A study of NASA satellite data, overlaid with reported cancer statistics, has identified nighttime exposure to lighted areas as a risk factor for breast cancer:

Women who live in neighborhoods with large amounts of nighttime illumination are more likely to get breast cancer than those who live in areas where nocturnal darkness prevails, according to an unusual study that overlaid satellite images of Earth onto cancer registries.

"By no means are we saying that light at night is the only or the major risk factor for breast cancer," said Itai Kloog, of the University of Haifa, who led the new work. "But we found a clear and strong correlation that should be taken into consideration."

The mechanism of such a link, if real, remains mysterious, but many scientists suspect that melatonin is key.

A tumor suppressing hormone long known to be impacted by the nighttime illumination, melatonin requires darkness for its synthesis and release:

Melatonin is a neurohormone produced in the brain by the pineal gland, from the amino acid tryptophan. The synthesis and release of melatonin are stimulated by darkness and suppressed by light, suggesting the involvement of melatonin in circadian rhythm and regulation of diverse body functions.

The study has not recommended melatonin supplementation. Not enough is known about the melatonin connection. Further studies will be required.

According to the Washington Post, the World Health Organization has been studying the hormonal impact of nighttime illumination, focusing on breast cancer rates among female night shift workers. When the studies revealed a 60% greater incidence of breast cancer among nurses, flight attendants and others, they classified such night shift work as a possible carcinogen. Work with laboratory rats have also produced similar results. Those who were kept in illuminated cages showed a higher incidence of cancer, whereas those in darkened cages do not.

The study looked at both breast cancer and lung cancer rates against the satellite data as a control point. Lung cancer is not thought to be impacted by illumination. The study bore out the difference in the statistics. Breast cancer was more prevalent in illuminated areas.

"The study has limitations," including not measuring levels of indoor lighting, "but it supports the overall idea," [Jim] Burch, [a University of South Carolina epidemiologist and biostatistician], who found the study "fascinating," said. "I think there is enough evidence to suggest we ought to be thinking about this more carefully."

Outside illumination, as well as "blue" type light (i.e. computer screens), are seen as melatonin suppressors. In addition, there is concern that the new, more energy efficient compact fluorescent bulbs, which are more suppressive than incandescent bulbs, may be an impact, as well.